Businessman and real estate developer Donald Trump (L) greets U.S. Republican presidential candidate and former Massachusetts Governor Mitt Romney after endorsing his candidacy for president at the Trump Hotel in Las Vegas, Nevada in this February 2, 2012 file photo. REUTERS/Steve Marcus

The Fox News Channel-sponsored debate began as a free-for-all fracas with tension mounting over Trump's ascendancy and his drive to become the presumptive nominee should he win nominating contests in Florida and Ohio on March 15.

At center stage, Trump was asked to respond to Romney's criticism that the billionaire real estate developer would lead the country into a recession, would weaken the United States on national security and had failed to properly disavow an endorsement from a former grand wizard of the Ku Klux Klan, a white supremacist group.

Trump called Romney a failed candidate. He said he would launch a rewrite of trade deals that he said favored China and Mexico. He also said he had disavowed the KKK endorsement.

But the debate quickly went down a negative path when Trump responded to rival Marc Rubio's contention last month that Trump had "small hands."

"Look at these hands," Trump said, flashing his two hands to the crowd. To the suggestion that he might be small elsewhere, Trump said: "I guarantee you there is no problem."

Trump was joined on stage at the Fox Theatre by his three remaining rivals, Rubio, a U.S. senator of Florida, U.S. Senator Ted Cruz of Texas and Ohio Governor John Kasich.

It's a far smaller field than the 17 Republican candidates that began the race for the 2016 presidential nomination, but one that is still splintered between the incendiary New York businessman and three experienced politicians.

The debate was the candidates' first face-to-face gathering since Super Tuesday nominating contests this week gave extra momentum to Trump but did not knock out his rivals.

Mainstream figures in the party are seeking a strategy to halt Trump's march to the nomination for the Nov. 8 election to succeed Democratic President Barack Obama.

Some party leaders and donors are critical of Trump's positions on trade and immigration, including his calls to build a wall between the United States and Mexico, deport 11 million illegal immigrants and temporarily bar Muslims from entering the country.

At the debate, Trump, 69, was questioned for the first time since last year by Fox News anchor Megyn Kelly, who angered him with her questioning at the Republicans' first debate on Aug. 6, prompting him to cancel participation in a debate in Iowa in January, a move that appeared to cost him some votes.

The debate took place hours after 2012 Republican nominee Romney gave a blistering speech about the dangers of choosing Trump. He called Trump a phony and a fraud who has failed in many business ventures despite his touted success.

The Detroit debate was one more opportunity for Rubio and Cruz to try to slow Trump's momentum. They are the last two anti-Trump candidates standing in what has been a bruising nomination battle. Kasich has largely steered clear of the anti-Trump effort and tried to remain above the fray.

Rubio went on the attack against Trump at the last debate on Feb. 25 and has tried to establish himself as the main Trump alternative by labeling him as a "con artist" who has escaped serious vetting by a news media fixated on his star power and brash rhetoric.